For the provision of vacuum for a pneumatic brake booster, the inner space of which is subdivided into at least one vacuum chamber and one working chamber, vacuum pumps are employed which suck in residual air from the vacuum chamber and eject into the atmosphere. For this purpose, as a rule, vane-cell pumps or swing-vane pumps are used in the automobile industry. These have, as a consequence of the principle adopted, a large amount of friction and must be lubricated in order to achieve an acceptable service life. Vacuum pumps with vanes which are driven by the internal combustion engine of the motor vehicle are therefore connected to the oil circuit of the internal combustion engine. Nevertheless, an appreciable fraction of the power output by the internal combustion engine has to be expended in order to drive such a pump. This is true even when the vacuum is already fully formed in the chamber to be evacuated. It is therefore expedient to operate the vacuum pump with electrical energy and to switch it on only when the absolute pressure in the vacuum chamber rises above a predetermined value.
Furthermore, in vehicles with an electric or hybrid drive, the vacuum pump cannot be driven or temporarily cannot be driven by the internal combustion engine. In these vehicles, therefore, electrically driven vacuum pumps are employed.
Equipping such an electrically driven pump with a lubricant circuit or connecting it to such would entail a disproportionally high outlay. Only dry-running vacuum pumps can therefore be considered for use in motor vehicles having brake systems with an electrically driven vacuum pump. For this purpose, in vane-cell pumps, the self-lubricating material used is graphite, from which the vanes are produced with required precision at high outlay. Efforts therefore tend towards using a diaphragm pump for the electrical provision of a brake vacuum.
Diaphragm pumps are generally known. DE 35 29 978 A1, which is incorporated by reference, discloses a motor/pump assembly comprising a double-diaphragm pump with a rotating eccentric shaft which is driven by an electric motor.
The automobile industry stipulates very stringent requirements with regard to the acoustic comfort of the motor vehicle components, and robust long-life pumps with very low noise emissions are demanded from the manufacturers. On account of vibrations, the known diaphragm pumps mostly cannot fulfil these requirements or demand a high outlay in terms of sound-damping measures.